It is well known that the temperature of a laser diode must be closely controlled to operate the laser within precise tolerances for both wavelength and power. A so-called ThermoElectric Cooler (TEC) is often used for this purpose since a TEC can be controlled to either add or extract heat from a laser depending on whether the desired operating temperature is above or below the ambient temperature. Typical temperature controlled packages for laser diodes that use a TEC can control device internal temperatures ranging from about 0–70 degrees Centigrade.
In some cases it is desirable to extend the temperature range over which the laser diode package can be controlled. For example, laser diode packages are often used in communication systems such as CATV systems. In CATV applications, high power laser diodes are often used in the forward transmission path from the headend to the cable subscriber. Other lower power (e.g., 2 mw) laser diodes are often used in the return path from a system node to the headend. The laser diodes are often located in system nodes that contain a variety of other components that generate significant quantities of heat. These components are typically in close proximity to one another to minimize the space occupied by the node. As a result, temperatures inside the node can reach up to about 90 degrees Centigrade. Since conventional laser diode packages are generally specified only up to about 70 degrees Centigrade, it is necessary to physically separate the package from the heat generating components in the node to reduce the temperature experienced by the package. Even in this case the TEC often operates near its maximum temperature differential, which not only reduces the efficiency of the TEC, but could also lead to thermal runaway, since the additional power needed to cool the laser diode may increase rather than decrease the temperature of the laser diode's operating environment, leading to catastrophic failure of the device. At the other temperature extreme, a lightly loaded system in a harsh environment at very low temperature may experience extreme low temperatures of −35 degrees Centigrade or below.
Accordingly, it would be desirable to provide a laser diode package whose temperature can be controlled over a greater range of temperatures.